The present invention relates generally to multipurpose filtering materials, and in particular, to the use of such materials in an electrostatographic reproducing apparatus.
In an electrostatographic reproducing apparatus commonly used today, a photoconductive insulating member may be charged to a negative potential, thereafter exposed to a light image of an original document to be reproduced. The exposure discharges the photoconductive insulating surface in exposed or background areas and creates an electrostatic latent image on the member which corresponds to the image areas contained within the original document. Subsequently, the electrostatic latent image on the photoconductive insulating surface is made visible by developing the image with a developing powder referred to in the art as toner. During development the toner particles are attracted from the carrier particles by the charge pattern of the image areas on the photoconductive insulating area to form a powder image on the photoconductive area. This image may be subsequently transferred to a support surface such as copy paper to which it may be permanently affixed by heating or by the application of pressure. Following transfer of the toner image to the support surface the photoconductive insulating surface may be discharged and cleaned of residual toner to prepare for the next imaging cycle.
Various types of charging devices are used in electrostatographic reproducing apparatus to provide precharge and charge functions with regard to the photoconductive insulating layer and also with regard to transferring the toner image from the photoreceptor to the transfer member, such as copy sheet and subsequently detacking the paper from the imaging surface so that it may be collected.
The operation of the corona discharge devices whether they be negative or positive discharge devices particularly at the higher levels of output corona result in the formation of a variety of noxious gases in the machine. It has long been known that the corona generator results in the formation of ozone in the atmosphere adjacent to the corona generator. Ozone is extremely reactive and can attack machine components as well as being toxic to humans. Relative low concentrations of ozone in the atmosphere, for example, from 1 part per thousand to 1 part per million can cause headaches, nausea, and irritation of mucous membranes. Further, as described in detail in U.S. Ser. No. 703,971, it has been recently found that corona discharge devices that produce a negative corona also produce various nitrogen oxide species which may interact in someway with the photoconductive layers resulting in poor copies. For example, it is believed that these nitrogen oxide species may be adsorbed by the conductive shield as well as the housing of the corona generating device and that, when the machine is turned off for an extended period of idleness, the absorbed nitrogen oxide species are gradually desorbed and interact with the photoconductive layers. It is believed that they in someway interact with the surface of the photoreceptor increasing the lateral conductivity so that it cannot retain a charge in image fashion to be subsequently developed with toner.
The severity of the problem is further compounded by the increased desire to make automatic reproducing apparatus increasingly compact so that various processing stations are enclosed within a smaller and smaller volume. As a result any harmful gaseous species generated by the corotrons tend to increase in concentration in the space within photoreceptor drum cavity.
The nitrogen oxide species tend to stay within the cavity around the drum and provide a loss in line density over time which is fairly perceptible in just a few hours. The problem is compounded in those applications where the drum cavity has an excessively long drum such as one which may be used for copying blueprints and the like in that the length of all the corona generating devices is correspondingly increased thereby dramatically increasing the volume of noxious gases that may be produced during corona generation.
As a result of this desire to further compact the machine in addition to generating excess ozone and other corona byproducts such as, a nitrogen oxide species mentioned above, other difficulties may be encountered. In particular, silicone oils are typically used as fuser release materials in the fuser system of electrostatographic reproducing apparatus and these are found to form what is believed to be oxide products in the form of whiskers on corotron charging devices which tend to reduce the charging efficiency. Furthermore it is possible that the heat generated from the fuser whether it be a fuser roll assembly or radiant fuser be at a level to overheat for the exposure lamp, the photoconductor, the cleaning blade since they are all positioned in such a small area that the heat produced by the fuser cannot escape.
In addition it is possible that some of the nitrogen oxide species generated by the corona generators may react with other materials in incoming air, for example, ammonia to form ammonium nitrates which tend to plate out on elements or surfaces critical to the imaging process.